Apart from the above, the Ironman events tend to be very time cut off based, presumably to keep it relatively elitist, so I wouldn’t expect a breast stroke swim to be fast enough unless you are very quick.
And then if your that fast at breast stroke, you should be more than capable of putting in a good front crawl time with the required practice.
I understand the problem as I too am crap at crawl. When I met the missus many years ago I could easily beat her over a couple of lengths as she got knackered too quickly.
She’s now on her umpteeth half ironman and can swim for miles using front crawl. I still blow after 2 lengths.
It is do-able, just takes time and dedication to learn.